FISH PREDATORS MAINTAIN ESTUARINE BIODIVERSITY AND BENEFIT ECOSYSTEM ENGINEERS A Dissertation by JOSEPH WILLIAM NEWTON LEO REUSTLE BS, University of California, Davis, 2013 Submitted in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY in MARINE BIOLOGY Texas A&M University-Corpus Christi Corpus Christi, Texas May 2020 © Joseph William Newton Leo Reustle All Rights Reserved May 2020 FISH PREDATORS MAINTAIN ESTUARINE BIODIVERSITY AND BENEFIT ECOSYSTEM ENGINEERS A Dissertation by JOSEPH WILLIAM NEWTON LEO REUSTLE This dissertation meets the standards for scope and quality of Texas A&M University-Corpus Christi and is hereby approved. Benjamin D. Walther, PhD Delbert L. Smee, PhD Chair Co-Chair Jeffrey W. Turner, PhD Jeremy L. Conkle, PhD Committee Member Committee Member Darek J. Bogucki, Degree Graduate Faculty Representative May 2020 ABSTRACT Loss of top predators may lead to the proliferation of mesopredators (i.e., intermediate consumers), with significant consequences for entire food webs. Termed mesopredator release, this process is typically attributed to a decline in the abundance of top predators. We investigated the potential for moderate environmental changes, that disrupt sensing abilities, to trigger mesopredator release by diminishing the foraging ability of top predators without affecting their abundance. In estuaries, fishes occupy the upper trophic levels and many species rely on visual cues to forage. We hypothesized that increased turbidity would attenuate fish foraging ability, increase the abundance of crabs and other mesopredators, and significantly alter coastal food webs. In oyster reef communities, turbidity triggered mesopredator release in 2016 and 2017, even though freshwater inflow and ambient salinity varied significantly between years, suggesting that turbidity’s effects on estuarine food webs are robust. Following experiments in 2017, our field site was struck by Hurricane Harvey, a category 4 storm. Oyster mortality was high following Harvey due to low salinity and trophic reliance on oysters as a basal resource. Hurricane Harvey removed human fishing pressure, causing fish populations to increase dramatically, resulting in stronger top-down control on crabs that are the primary predator of newly settled oysters. We also investigated the potential for barnacles as accessible and biologically relevant flow indicators since hydrodynamics are key regulators of species- interactions. In summary, fish predators are important components of oyster reef ecosystems, enhancing biodiversity and, at times, benefiting oysters through a trophic cascade depending on the environmental context. Turbidity and fishing reduce top down control by fishes, leading to v increases in the abundance of intermediate consumers, less diverse reef communities, and often damaging juvenile oysters. vi DEDICATION To All My Relations: Aho Mitakuye Oyasin. vii ACKNOWLEDGEMENTS I thank my Co-Chair, Dr, Lee Smee for the incredible support, puns, and knowledge he has shared with me over the years. I thank him for first seeing something in me and providing an environment where I could thrive. Even as we finished much of this dissertation hundreds of miles away from each other, he always made sure to make me feel like a priority and a valued member of the lab. In short, Lee has been a great mentor and has helped push me to improve as a scientist and beyond. I thank my Committee members: Dr. Benjamin Walther, Dr. Jeffrey Turner, and Dr. Jeremy Conkle for their direction, dedication, and sagacious knowledge. Thank you to my funding sources, including the NSF GRFP and the Texas SeaGrant Grants-in-aid of Graduate Research (Grant No. 619820-00021). "This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. 1645635. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation." I thank my fellow SACNISTAS and my TxARM/AGEP cohort. Thank you to the Center for Coastal Studies at TAMUCC for allowing me to spend countless hours at the work-bench picking through samples. Thank you to Chriss Shoppe for your patience in teaching us how to operate and trailer the boats. Thank you to Dr. Richard Coffin, who despite not being officially on my Committee, never missed the opportunity to mentor me as a researcher, educator, and a person. Rick has gone above and beyond more times than I can recount here. Rick has been an incredible mentor, advocate, and friend. viii Thank you to Dr. Carolyn Weaver for your steadfast support, wit, and mentorship. You helped keep me alive during field seasons and are a great source of wisdom and positivity. I thank the many MARB and CMSS Graduate students whom I have had the pleasure of interacting with throughout my tenure. Thank you to the SMEE lab. Without each of you, there’s no way I could have finished all of these projects. Specifically, I want to thank Meredith Diskin and Kelly Correia. We essentially all came in to the Smee lab at the same time and I am so proud of the work we have done. I thank you and look forward to seeing your great successes! I also want to specifically thank Dr. Jessica Lunt. Our oyster reef ecology work has aligned incredibly well, but I could not have done my work without you first setting the foundation. Thank you for all of your hard work, advice, and mentorship. I thank Dr. Avery Scherer, Dr. Kaitlyn Schroeder-Spain, Dr. Keith Johnson, and Dr. Scott Large. I have had many meaningful conversations with each of you that have helped to shape my research and future goals. Thank you for being the founding doctoral researchers from the SMEE lab and trailblazing to great careers. I would like to thank our fantastic Undergraduate researchers: Micah Bachner, Andrew Miller, Cody Myers, Cayla Carlson, and several others. Finally, thank you to my wonderful and supportive family. To my mother and father— thank you for being paragons of perseverance. I thank my siblings for their incredible support and unyielding excitement. I thank my wife Alex for having the patience to look through every figure, paper, and presentation, and for listening to my long-winded explanations. I thank Myla for being an “unconventional”, but eternally sweet and loyal dog. Lastly, I thank my daughter Claire. My sweetest memories of writing this dissertation were days spent writing with you by my side. I look forward to watching you grow, but will always cherish these early times. ix TABLE OF CONTENTS CONTENTS PAGE ABSTRACT .................................................................................................................... v-vi DEDICATION .................................................................................................................. vii ACKNOWLEDGEMENTS ............................................................................................. viii TABLE OF CONTENTS .....................................................................................................x LIST OF FIGURES .......................................................................................................... xii LIST OF TABLES ........................................................................................................... xiv INTRODUCTION ...............................................................................................................1 CHAPTER I: CLOUDY WITH A CHANCE OF MESOPREDATOR RELEASE: TURBIDITY ALLEVIATES TOP-DOWN CONTROL ON INTERMEDIATE PREDATORS THROUGH SENSORY DISRUPTION...................................................................................................9 ABSTRACT .............................................................................................................9 INTRODUCTION .................................................................................................10 METHODS ............................................................................................................13 RESULTS ..............................................................................................................20 DISCUSSION ........................................................................................................23 ACKNOWLEDGMENTS .....................................................................................31 REFERENCES ......................................................................................................32 CHAPTER II: TURBIDITY AND SALINITY INFLUENCE TROPHIC CASCADES ON OYSTER REEFS THROUGH MODIFICATION OF SENSORY PERFORMANCE AND FACILITATION OF DIFFERENT PREDATOR TYPES ................................................57 ABSTRACT ...........................................................................................................57 x INTRODUCTION .................................................................................................58 METHODS ............................................................................................................61 RESULTS ..............................................................................................................66 DISCUSSION ........................................................................................................68 ACKNOWLEDGEMENTS ...................................................................................72 REFERENCES ......................................................................................................73